The invention proceeds in this case from prior art as described, for example, by U.S. Pat. No. 3,610,476 A1. In rotary airlocks, blowing out at least the product chamber closest to the outlet of the rotary airlock using a flushing gas stream is accordingly known, to ensure that material possibly adhering in this airlock chamber is also flushed into the outlet.
The cited document blows a flushing gas stream into the airlock chamber from the side of the housing of the airlock, in order to flush it out when the airlock chamber is located closest to the outlet.
The disadvantage of the known arrangement is that a large-volume flushing gas stream is required to enable sufficient flushing of the airlock chamber. This flushing gas stream has to be provided using separate means. The branching off of a flushing gas stream from the overall conveying gas stream is complex and difficult to implement.
The flushing gas suffers a high pressure loss upon entry into the airlock chamber, because the geometry of the airlock only permits small passage gas cross sections.
Accordingly, the respective airlock chamber can only be flushed using a small-volume flushing gas stream.
A further rotary airlock having blowing device is known from the subject matter of DE 31 02 153 A1, in which the compressed gas supply takes place in parallel to the axis of rotation. The main criterion in this case is the reduction of the pulsation during the product discharge via the reduction of the outlet diameter. It is also difficult here to inject a sufficiently high flushing gas volume and a sufficient flushing gas pressure into the airlock chamber, because the flushing gas can only be introduced from the end face of the housing of the rotary airlock. Sufficient flushing of the airlock chamber over the entire length of the airlock chamber is not possible in this arrangement. In the cited document, it is moreover the focal point that in principle a leaked gas stream is used for flushing. However, because the leaked gas is very small in volume, only a minor flushing effect of the airlock chamber also occurs. The blowing out effect of the airlock chamber is accordingly inadequate.
Similar prior art is disclosed in GB 2 129 935 A, in which the compressed air supply takes place in parallel to the axis of rotation, but the blowing out takes place tangentially in relation to the airlock chamber. The disadvantage also exists here that flushing can only be performed using a small flushing gas volume and low pressure.
US 2005/026 93 69 A1 relates to gas-permeable airlock chamber delimitations or airlock webs, which are to be permeated by a gas stream, wherein the gas stream is injected in parallel to the axis of rotation of the airlock. The flushing effect is inadequate, because the gas-permeable material has to be penetrated using specific gas-guiding boreholes, in the case of which, however, the risk exists that these boreholes will clog with the particulate material of the mass product stream. Therefore, a risk of clogging exists in such an airlock having gas-permeable airlock webs. Thus, only baked-on deposits in the region of the airlock webs are to be prevented; an actual blowing out effect is not ensured.